docs: def print_curation_tree(self, unit_id):
          '''This function prints the current curation tree for the unit_id (roots are current unit ids).
  
          Parameters
          ----------
          unit_id: in
              The unit id whose curation history will be printed.
          '''
          root_ids = []
          for i in range(len(self._roots)):
              root_id = self._roots[i].unit_id
              root_ids.append(root_id)
          if(unit_id in root_ids):
              root_index = root_ids.index(unit_id)
              print(self._roots[root_index])
          else:
              raise ValueError("invalid unit id")